Abstract: A concentration method and concentrator arrangement enable a plurality of synchronous or asynchronous data terminals to be served by a common B channel of an ISDN to which the data terminals are connected by a digital subscriber termination and terminal adapters for transmission in packet mode. The terminal adapters are connected to the digital subscriber termination at the S0 basic access level. In the event of a request for B channel communication between a first data terminal served by a first terminal adapter and a packet mode ISDN port to which a second data terminal already has access via a second terminal adapter and via a first B channel, a transit connection is established between the two terminal adapters via the digital subscriber termination using a second B channel. Data packets conveyed between the first data terminal and the ISDN port are conveyed via the terminal adapter of the second data terminal.

Abstract: A synchronizing system for a private digital exchange (1) comprising a logic control unit (4) and specialized interfaces (9, 8) whereby the exchange is connected firstly to a plurality of subscriber terminals (2) via SO accesses, and secondly to a telecommunications network (3) via TO base accesses. The exchange includes a time base (6) which associates a fixed frequency local oscillator (7) with a phase locked loop (32). The system includes clock switching means suitable for imposing the first clock signals to come from the network (3) via an active one of the TO base accesses and the associated interface (8) on the phase locked loop (32) of the time base (6) as soon as said first clock signals come close in phase to the substitute clock signals provided by the time base (6) in the absence of said first signals from the network.